hhiiilH ho/ 1 !/ tuMaal/ chare r\icf*f\\tat*
build, hack, tweak, share, discover,-
Written By: Ashley Franks
(optional) if drilling your own lids
(optional) for testing power
Pair of Rubber Gloves (1)
Shovel or Trowel (1)
Wire strippers (1)
(optional) if not using pre- stripped wires
from the kit
MudWatt MFC Kit (1)
Item #MKKT01 from Maker Shed $45.
Includes all materials below, except
mud. You can also build MFCs from
scratch, minus the Hacker Board.
sized to seal marine wire through holes
drilled in container lid
MuddWatt Hacker Board (1)
includes voltage- boosting chip. 8- pin
socket. 22[xF capacitor, resistors, and
red LED that blinks when bacteria
generate power. (NOTE: some of the
photos show the MuddWatt Explorer
Almost any mud with organic
compounds will work. Try freshwater
ponds or streams, brackish swamps and
inlets, or saltwater marshes. Try to find
© Make Projects
Page 1 of 6
mud that bubbles when disturbed or
smells like rotten eggs — both are good
indicators of anaerobic bacteria (but
don't worry, your MFC won't smell). You
can also use soil (just dig down a foot)
or compost from the warm middle of a
Marine Wire (2 lengths)
Using 2 different colors helps.
Microorganisms often get a bad name because some of them cause disease. But many have
useful abilities, from making beer, cheese, and wine to processing waste and cleaning up
toxic chemicals. One type of bacteria, discovered in 1987 by Derek Lovley, can generate
electricity. Here's how you can find bacteria like these in a local pond and put them to work.
Most non-photosynthesizing bacteria, like all animals, get their energy from the cellular
respiration process, which converts glucose and oxygen to water and carbon dioxide.
Oxygen works as an oxidizer, which means it accepts electrons as it combines with other
chemicals in reactions. But special bacteria underground have no oxygen to breathe.
Instead, they produce energy for their growth by transferring electrons to clumps of rust and
other surrounding metal oxides, in a process called dissimilatory metal reduction. We now
know that these electric bacteria are found in mud virtually everywhere on Earth, as well as
in soil and compost heaps.
A microbial fuel cell (MFC) does the same thing as a battery: drive electrons from an anode
to a cathode through chemical oxidation/reduction reactions. What makes MFCs different is
that they run on organic substrate and bacteria.
"Metal-breathing" (Geobacter) bacteria at the anode carry out the oxidation reaction,
converting plant and animal debris in the mud into electricity and carbon dioxide. Electrons
flow through wires to a cathode sitting in water above the mud, where they combine with
oxygen to complete the circuit. The bacteria are highly efficient in this arrangement and can
produce electricity continuously for many months or even years.
© Make Projects www.makeprojects.com Page 2 of 6
Experimental MFC- powered buoys now operate in the Potomac River, using naturally
occurring bacteria in the mud to measure and transmit meteorological data.
These "Benthic Unattended Generators" (BUGs) have worked for several years with no
decrease in power output (see http://nrl . navy . mi l/code6900/bug ) . Geobacter species
possess other useful abilities, such as the ability to respire radioactive uranium and remove
it from ground water. They have proven versatile and effective in cleaning up areas
contaminated with uranium or organic pollutants.
In addition to their scientific interest, MFCs are a useful educational tool: a popular science
project that encompasses microbiology, chemistry, electronics, and other disciplines. That's
why Keego Technologies developed the MudWatt, a low-cost microbial fuel cell kit. They
also support online discussion forums for MFC makers.
With the MudWatt, students of all ages are learning about MFCs and making scientifically
relevant discoveries. For example, a 6th-grade student in Santa Cruz uncovered (literally) a
river sediment that produces twice as much power as typical topsoil.
© Make Projects www.makeprojects.com Page 3 of 6
Step 1 — Make your own MFC.
• Mix your mud (or soil or compost) to saturation with water and put a V2" layer into the
bottom of your container. You can experiment by adding extra ingredients; see
http://keegotech.com/community/education for ideas.
• Cut the 2 pieces of graphite fiber cloth to fit the container. Be careful not to disperse the
fibers in the air because they can cause short circuits in household electrical equipment.
• Strip 4" from one end of each piece of marine wire, and weave each through a piece of
graphite cloth. Strip the other ends V2" and thread each through a grommet. Drill the lid of
the container to fit the grommets.
• Lay one graphite cloth on top of the mud with its wire sticking up; this will be the anode.
Cover it with V2" more mud and let it settle for a few minutes.
© Make Projects
Page 4 of 6
• For the cathode, place the other graphite cloth on top of the mud, with its wire also pointing
up. Avoid covering the cathode cloth with any mud, and gently pour a little water on top to
• If the cathode doesn't sink in water (it may have air bubbles in it), try putting a few small
rocks on it to keep it from floating.
• Close the container, sealing the grommets into the holes in the lid such that the wires stick
out. It may help to gently twist the wires counterclockwise one turn before screwing on the
• Attach the 2 wires to the MudWatt Hacker Board's 8-pin socket: anode to the (-) pin and
cathode to the (+) pin.
# Attach the Hacker Board to the lid of your container using the provided adhesive pad.
© Make Projects
Page 5 of 6
Step 5 — Microbe Power
• Within 3-10 days, the MFC will generally produce enough power to make the LED blink;
the more power, the faster the blinking. Keep your MFC warm and moist inside to help
the bacteria grow and produce the most power.
• Try adding a very small amount of table salt to the water to increase conductivity if
the voltages are too low.
• The MudWatt Hacker Board boosts the bacteria's power to 2.4 volts, and its 8-pin
socket lets you change a resistor value in the blinker circuit to optimize power to the
LED. You can also power other devices that run on 3V or less. Download the
instructions at http://keegotech.com/community/Hacker Bo. . . and see
http://keegotech.com/forum for more ideas.
• Power generated by an MFC is a product of its electrode surface area, so once you
have your first one running, don't be afraid to go large.
• By simply configuring 2 electrodes correctly in mud, soil, or compost, anyone anywhere
can harness naturally occurring bacteria to provide continuous, non-polluting, carbon-
This project first appeared in MAKE Volume 30 , page 140.
This document was last generated on 201 2-1 0-30 07:00:38 PM.
© Make Projects
Page 6 of 6